Make the amount of IO parallelism configurable (i.e. number of separate
index sections to be processed in parallel).
Defining PARALLEL_IO = 20 restores approximately the IO pattern of the
original preload_index() implementation. Best performance is achieved with
PARALLEL_IO = 1 (i.e. sequential IO).
Signed-off-by: Karsten Blees <bl...@dcon.de>
---
Applies on top of "preload-index: optimize for sequential IO".
preload-index.c | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)
diff --git a/preload-index.c b/preload-index.c
index 6ac368d..5fe5521 100644
--- a/preload-index.c
+++ b/preload-index.c
@@ -23,6 +23,7 @@ static void preload_index(struct index_state *index,
*/
#define MAX_PARALLEL (20)
#define THREAD_COST (500)
+#define PARALLEL_IO (1)
struct thread_data {
pthread_t pthread;
@@ -38,23 +39,34 @@ static void *preload_thread(void *_data)
struct thread_data *p = _data;
struct index_state *index = p->index;
struct cache_def cache;
+ int blocks = DIV_ROUND_UP(index->cache_nr, THREAD_COST);
+ int step = DIV_ROUND_UP(blocks, PARALLEL_IO);
memset(&cache, 0, sizeof(cache));
for (;;) {
/* get next batch of entries to check */
pthread_mutex_lock(p->pmutex);
nr = *p->pnr;
- *p->pnr += THREAD_COST;
+ (*p->pnr)++;
pthread_mutex_unlock(p->pmutex);
+ /* break loop if no more work to do */
+ if (nr >= blocks + PARALLEL_IO - 1)
+ break;
+
+ /*
+ * rearrange iteration order, i.e. with PARALLEL_IO = 2,
+ * [0, 1, 2, 3, 4, 5, 6, 7] becomes [0, 4, 1, 5, 2, 6, 3, 7]
+ */
+ nr = (nr / PARALLEL_IO) + (nr % PARALLEL_IO) * step;
+ if (nr >= blocks)
+ continue;
+ nr *= THREAD_COST;
+
max_nr = nr + THREAD_COST;
if (max_nr > index->cache_nr)
max_nr = index->cache_nr;
- /* break loop if no more work to do */
- if (nr >= max_nr)
- break;
-
for (; nr < max_nr; nr++) {
struct cache_entry *ce = index->cache[nr];
struct stat st;
--
1.9.4.msysgit.0.1.gc8a51b4
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